# Diamond-Square (#198)

**URL:** <https://www.ruby-forum.com/t/diamond-square-198/164083>\
**Category:** Ruby\
**Created:** [March 27, 2009, 5:57pm UTC](https://www.ruby-forum.com/t/diamond-square-198/164083 "2009-03-27T17:57:27Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![danmcb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/13edae/32.png) [@danmcb](https://www.ruby-forum.com/u/danmcb)\
**Post date:** [March 27, 2009, 5:57pm UTC](https://www.ruby-forum.com/t/diamond-square-198/164083/1 "2009-03-27T17:57:27Z")

</div>

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

The three rules of Ruby Q.:

1. Please do not post any solutions or spoiler discussion for this  
quiz until 48 hours have elapsed from the time this message was  
sent.

2. Support Ruby Q. by submitting ideas and responses  
as often as you can!  
Visit: [http://rubyquiz.strd6.com/suggestions](http://rubyquiz.strd6.com/suggestions)

3. Enjoy!

Suggestion: A [QUIZ] in the subject of emails about the problem  
helps everyone on Ruby T. follow the discussion. Please reply to  
the original quiz message, if you can.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

## Diamond-Square (#198)

Guten Tag Rubyists,

Following in the same vein as last week’s quiz I present to you the  
[diamond-square algorithm](http://gameprogrammer.com/fractal.html#diamond). Instead of one dimensional terrain as  
last week, the random terrain generated by this algorithm is in two  
dimensions. Visual displays are again encouraged.

The secret to this algorithm is that there are two phases for  
generating the new random values: from the diagonals (diamond) and  
from the adjacents (square). This makes the generated terrain smoother  
and prevents artifacts from generating solely by the adjacents.

Once equipped with these terrain generation algorithms, making ruby  
based Elf/Goblin/Tanks simulations will be a breeze!

There is now a suggestion form up on the Ruby Q. website:  
[http://rubyquiz.strd6.com/suggestions](http://rubyquiz.strd6.com/suggestions) . I’m looking forward to all of  
your great suggestions!

Have Fun!

---

<div class="post-metadata">

**Author:** ![danmcb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/13edae/32.png) [@danmcb](https://www.ruby-forum.com/u/danmcb)\
**Post date:** [April 6, 2009, 6:25am UTC](https://www.ruby-forum.com/t/diamond-square-198/164083/2 "2009-04-06T06:25:34Z")

</div>

Since there were no solutions submitted on the mailing list this week  
I’ve included a solution of my own.

```
class DiamondSquare
  def self.rando
    rand() - 0.5
  end

  def self.go(times)
    arrays = [[0.5]]

    ratio = 2

    times.times do
      arrays.map! do |array|
        insert_nils(array)
      end
      arrays = insert_arrays(arrays)
      compute_from_diagonals(arrays) {|a, b, c, d| (a + b + c +

```

d)/4 + rando_ratio}  
compute\_from\_adjacents(arrays) {|a, b, c, d| (a + b + c +  
d)/4 + rando_ratio}  
ratio \*= 0.5  
end

```
    return arrays
  end

  def self.insert_arrays(arrays)
    new_arrays = []
    arrays.size.times do |i|
      array = arrays[i]
      new_arrays.push array, Array.new(array.size, 0.0)
    end
    return new_arrays
  end

  def self.insert_nils(array)
    new_array = []
    array.size.times do |i|
      new_array.push(array[i], 0.0)
    end
    return new_array
  end

  def self.compute_from_adjacents(arrays)
    n = arrays.size
    n.times do |row|
      n.times do |col|
        next if (row + col) % 2 == 0
        arrays[row][col] =
          yield(arrays[(row-1)%n][col], arrays[row][(col-1)%n],
                arrays[row][(col+1)%n], arrays[(row+1)%n][col])
      end
    end
  end

  def self.compute_from_diagonals(arrays)
    n = arrays.size
    n.times do |row|
      next if row % 2 == 0
      n.times do |col|
        next if col % 2 == 0
        arrays[row][col] =
          yield(arrays[(row-1)%n][(col-1)%n], 

```

arrays[(row-1)%n][(col+1)%n],  
arrays[(row+1)%n][(col-1)%n],  
arrays[(row+1)%n][(col+1)%n])  
end  
end  
end

```
  def self.print_arrays(arrays)
    i = 0
    arrays.each do |array|
      print "%4d: " % i
      array.each do |ele|
        print '%1.3f ' % ele
      end
      i += 1
      puts
    end
    puts '---------------------------------------'
  end
end

```

I actually wrote it almost a year ago to generate the terrain for  
[Dungeon Farmer](http://code.google.com/p/strd6/wiki/DungeonFarmer). It’s kind of clunky, but it has its merits. Some  
of the interesting things about this solution are that rather than  
start with a full sized array it starts with a small array (very small  
actually, 1x1) and inserts empty elements to be filled in before each  
step. This causes the array to double in width and height at each  
iteration.

The `compute_from_diagonals` and `compute_from_adjacents` methods  
yield the four adjacent or diagonal cells so that you can easily  
change the nature of the computation. The cells wrap around in a  
toroidal manner to make it easy to compute the values on the edges.

It was fun to make and I hope you find it interesting!